A high-pressure EGR device takes an EGR gas from a portion in an exhaust passage on an upstream side of a turbine and puts the EGR gas back to a portion in an intake passage on a downstream side of a compressor. In order to reduce NOx (nitrogen oxides) contained in an exhaust gas from a supercharged engine, a low-pressure loop EGR device to replace the high-voltage loop EGR device is under development in recent years (see PTL 1 or PTL 2) from the viewpoint of ensuring a sufficient EGR quantity, and so forth. Such a low-pressure loop EGR device is configured to take an EGR gas from a portion in an exhaust passage on a downstream side of a turbine and to put the EGR gas back to a portion in an intake passage on an upstream side of a compressor.
The low-pressure loop EGR device includes an EGR passage (an EGR pipe). The EGR passage connects the portion in the exhaust passage on the downstream side of the turbine to the portion in the intake passage on the upstream side of the compressor to communicate between the portions, thereby enabling the EGR gas to communicate (flow) between these portions. In addition, an EGR valve is provided midway in the EGR passage. The EGR valve opens and closes the EGR passage. An EGR cooler is provided midway in the EGR passage at a portion closer to the exhaust passage than the EGR valve. The EGR cooler cools the EGR gas.
Accordingly, when the EGR valve opens the EGR passage while the supercharged engine is in operation, part of the exhaust gas in the exhaust passage flows as the EGR gas from the portion in the exhaust passage on the downstream side of the turbine into the EGR passage. The EGR gas flowing into the EGR passage is once cooled by the EGR cooler, and then flows from the inside of the EGR passage to the portion in the intake passage on the upstream side of the compressor. Thereby, a combustion temperature in the supercharged engine drops and an amount of emission of NOx (nitrogen oxides) is reduced as a consequence.